Layered polymer on aluminum stacked capacitor

ABSTRACT

The present invention provides a capacitor having a plurality of layers of aluminum foil connected to a first electrical terminal of the capacitor and another plurality of layers of aluminum foil connected to a second electrical terminal of the capacitor. The layers of aluminum foil are separated by a polymer such as a conductive organic polymer, so that each layer of polymer physically separates a layer of aluminum foil connected to the first terminal from a layer of aluminum foil connected to the second terminal. In some such embodiments the aluminum foil may be etched to provide greater surface area and capacitance, and also may be oxidized to form a dielectric layer.

[0001] This application is a continuation of U.S. patent applicationSer. No. 09/922,965, filed Aug. 6, 2001, which is incorporated herein byreference in its entirety.

FIELD OF THE INVENTION

[0002] The invention relates generally to electronic capacitors, andmore specifically to foil stacked capacitors using aluminum and polymer.

BACKGROUND OF THE INVENTION

[0003] Electrical circuits often include capacitors for various purposessuch as filtering, bypassing, power decoupling, and to perform otherfunctions. High-speed digital integrated circuits such as processors andcomputer chipsets in particular typically perform best when the powersupplied to the integrated circuit is filtered with a capacitor placedphysically close to the integrated circuit.

[0004] Such power decoupling capacitors function to smooth outirregularities in the voltage supplied to the integrated circuits, andso serve to provide the integrated circuits with a more ideal voltagesupply.

[0005] By placing the decoupling capacitors near the integrated circuit,parasitic impedances such as printed circuit board path resistance orinductance are minimized, allowing easy and efficient transfer of energyfrom the decoupling capacitor to the integrated circuit. Minimization ofseries resistance and inductance in the capacitor itself is alsodesirable for the same purposes, and results in a more efficient anddesirable decoupling or bypass capacitor.

[0006] The internal series resistance of the capacitor is typicallyknown as the Equivalent Series Resistance, or ESR. Similarly, internalseries inductance is known as Equivalent Series Inductance, or ESL. Bothof these parameters can be measured for a given capacitor, and are amongthe basic criteria used to select capacitors for applications such asintegrated circuit power supply decoupling.

[0007] Past efforts to minimize ESL and ESR have included solutions suchas using multiple types of capacitors in parallel or combinationseries-parallel configurations, configured to product the desiredcapacitance at the very low ESR and ESL levels required. For example,tantalum capacitors in the order of 4.7 uF in parallel with 0.01 uFceramic chip capacitors were often sufficient for lower-speed digitallogic circuits of previous decades. But, new high speed digital logiccircuits such as high-performance computer processors require bothgreater capacitance because of the amount of power dissipated, and lowerESR and ESL because of the very high speeds at which the processorsoperate.

[0008] It is also desirable for capacitors to have a physically smallsize, so that they do not take an unduly large amount of printed circuitboard space. This is why space efficient capacitor technologies such astantalum and electrolytic capacitors are often implemented in circuitsdespite typically having relatively high inductance, resistance,dielectric absorption, and other unfavorable characteristics. Mitigationof unfavorable capacitor characteristics of electrolytic or tantalumcapacitors often also requires use of parallel capacitors with morefavorable characteristics as secondary or supplemental decouplingcapacitors.

[0009] What is desired is a single capacitor design that provides lowESR and ESL with large capacitance, and that is physically compact.

BRIEF DESCRIPTION OF THE FIGURES

[0010]FIG. 1 shows a side view of a aluminum foil and polymer capacitorwith opposing connected layers, consistent with an embodiment of thepresent invention.

[0011]FIG. 2 shows a surface mount capacitor package, consistent with anembodiment of the present invention.

[0012]FIG. 3A shows a multitermination surface mount technology (SMT)capacitor package, consistent with an embodiment of the presentinvention. The paragraph beginning at page 2, line 24 is added asfollows:

[0013]FIG. 3B shows a multitermination surface mount technology (SMT)capacitor package, consistent with an embodiment of the presentinvention.

[0014]FIG. 4 shows an aluminum foil and polymer capacitor havingmultiple conductive aluminum foil strips per layer, consistent with anembodiment of the present invention.

[0015]FIG. 5 shows an aluminum foil and polymer capacitor havingmultiple conductive aluminum foil strips per layer and further havingalternate orientation of adjacent layers of aluminum foil strips,consistent with an embodiment of the present invention.

DETAILED DESCRIPTION

[0016] In the following detailed description of sample embodiments ofthe invention, reference is made to the accompanying drawings which forma part hereof, and in which is shown by way of illustration specificsample embodiments in which the invention may be practiced. Theseembodiments are described in sufficient detail to enable those skilledin the art to practice the invention, and it is to be understood thatother embodiments may be utilized and that logical, mechanical,electrical, and other changes may be made without departing from thespirit or scope of the present invention. The following detaileddescription is, therefore, not to be taken in a limiting sense, and thescope of the invention is defined only by the appended claims.

[0017] The present invention utilizes aluminum foil and conductivepolymer in a stacked alternating layer configuration to provide low ESRand ESL parameters and high capacitance in a physically compact design.The present invention eliminates in some applications the need to usemultiple capacitors in parallel to achieve the desired level ofperformance, and is therefore also more easily located near a processoror other device for bypass applications. The reduction in circuit boardspace and cost as well as increased decoupling performance and betterperformance at high clock rates.

[0018]FIG. 1 illustrates a stacked capacitor configuration, as may beused to practice the present invention. Electrical terminal 101 isconnected to a first set of aluminum foil layers, each of which isseparated from an aluminum foil layer in a second set connected to asecond electrical terminal102 by a polymer 103. The polymer 103 may bean organic polymer, and in embodiments of the invention where aluminumfoil layers of at least one pole are oxidized to form a dielectricbarrier may be conductive polymers that are applied in contact with thefoil layers. Because the polymer and foil construction of someembodiments of the invention does not have any polarity-specificfeatures, the polarity of the first and second electrical terminals orpoles of these embodiments is not determined by the capacitor design.These capacitors may therefore be electrically connected without regardto terminal polarity, unlike tantalum, electrolytic, and some othercapacitor technologies commonly used in bypass or decouplingapplications.

[0019]FIG. 2 shows a surface mount capacitor package, as may be used toimplement some embodiments of the present invention. The capacitor isencased in a package 201 that may be a solid polymer, an epoxy, or othermaterial that physically holds or supports the capacitive elements suchas shown in FIG. 1. The capacitor is connected to external circuitry viaelectronic leads or terminations 202 and 203. Typically, such acapacitor will be placed on a printed circuit board and soldered viareflow soldering or a similar method to conductive pads and traces onthe circuit board. The leads 202 and 203 in the present invention neednot be polarized such that one particular lead must be connected to apositive voltage with respect to the other, but nevertheless may in someembodiments of the invention be polarized.

[0020]FIG. 3 illustrates an advanced implementation of the presentinvention using a multiterminal surface mount technology (SMT) packageto house and connect the capacitor. The eight-terminal SMT package iscommonly used for housing multilayer ceramic capacitors, and so is acommon form factor and easily integrated into printed circuit boarddesigns. Other variations of such a package exist and are within thescope of this invention, such as a package having terminations on morethan two sides of such a device. Similarly, larger packages such as astandard dual in-line package (DIP) may be used to house and connect thecapacitor.

[0021] In the particular embodiment of the present invention illustratedin FIG. 3, the multiterminal SMT package 301 contains a conductive sheetof aluminum foil 302. The aluminum foil for any given layer is connectedeither to the positive terminals or to the negative terminals of themultiterminal SMT package, as shown at 301 and 305. At 301, the aluminumfoil 302 is connected only to negative terminals such as shown at 303,and not to the positive terminals 304. At 305, an aluminum sheet ofopposite polarity in the capacitor is connected only to positiveterminals and not to negative terminals. Alternating positive andnegative layers of aluminum foil are stacked on top of each other inalternating fashion, each separated by a polymer layer, forming acapacitor similar to the capacitor illustrated in FIG. 1.

[0022] The design of the capacitor of FIG. 3 is calculated to reduce theequivalent series inductance (ESL) of the capacitor, allowing it toprovide current flow as a bypass capacitor more rapidly than otherhigher ESL designs. More specifically, the use of multiple terminals forthe positive and negative connections to the corresponding alternatinglayers of aluminum foil in the capacitor reduces ESL, as does drivingthe alternating layers of foil in the capacitor in an opposite physicaldirection to the layers immediately above and below each layer ofaluminum.

[0023] In some embodiments of the invention, the aluminum foil may beetched to increase the surface area of the aluminum foil. Application ofa conductive polymer or organic polymer to the etched foil provides aconductive path between the alternating etched aluminum foil capacitiveplates, and therefore facilitates a higher capacitance than would bepossible using other technologies. Formation of aluminum oxide (A1 ₂O₃)or other dielectric on the aluminum foil layers of at least one pole ofthe capacitor provides the dielectric component of the capacitor, andthe organic polymer effectively acts as an extension of a conductivepole of the capacitor. Further, such a capacitor configuration has thedesirable property of self-healing, or self-forming a dielectric barrierin places within the capacitor where the dielectric is damaged or hasimperfections and electricity is conducted between the poles of thecapacitor.

[0024] The polymer of the present invention is deposited in someembodiments onto very thin aluminum foil, which may be cut into stripsor other shapes such as shown in FIG. 3. These strips or shapes can bestacked in alternating layers, such that the alternating layers areattached alternately to a first or second terminal of the capacitor. Thecapacitors of the present invention need not be polarized, but in someembodiments may be polarized such that a positive terminal or anode mustbe connected to a higher voltage than a negative terminal or cathode.

[0025] Because the capacitor of the present invention is configured in aflat package configuration with multiple layers of foil connected toeach pole, it may be packaged in a number of other common formatpackages traditionally used for other purposes. Examples include EIAspec MLCC or tantalum format capacitor-style packages, which aretypically used for various other capacitor technologies such as stackedceramic and tantalum capacitors. Other multiterminal packages havingmore than two terminals may again be utilized to provide multipleconnections to each pole of the capacitor, providing potential benefitsin realized ESL and ESR reduction.

[0026]FIG. 4 illustrates another possible configuration consistent withthe present invention, including separating aluminum strips and drivingalternating strips within a single layer from different pole connectionpoints, further reducing ESL over configurations such as are shown inFIG. 1. For each strip of a certain layer and pole such as 401, which isconnected here to positive pole 402, at least one neighboring strip 403is connected to a pole of the same polarity but on the opposite side ofthe capacitor such as 403 is connected to pole 404.

[0027] In this example, the layer immediately above or below the layerhaving strips 401 and 403 connected to positive poles comprisessimilarly alternating strips connected to negative poles. Morespecifically, strip 405 is directly under strip 401, and is separatedonly by the organic polymer and by the aluminum oxide dielectric on atleast one of the strips. Strip 405 is opposite in polarity from strip401, and is connected to a pole at the strip end opposite the end towhich strip 401 is connected to its respective opposite pole. Theterminals and alternating foil layers are not restricted to only twosides of a package or to two orientations using this format. Forexample, alternating and electrically opposing strips may be arranged orwoven into a four-sided format such as is illustrated generally in FIG.5 to further reduce ESL.

[0028] These configurations utilize multiple terminals for the positiveand negative connections to the corresponding alternating layers andstrips of aluminum foil in the capacitor, and therefore reduces the ESLof the capacitor. Also, driving the alternating layers of foil in thecapacitor in an opposite physical direction to the layers immediatelyabove and below each layer of aluminum further reduces ESL, making sucha configuration more able to quickly provide change in current flow toattached devices when used as a bypass capacitor in high-speed digitalcircuits or in other high-frequency applications.

[0029] Because the various embodiments of the invention address the needfor reduced ESL and ESR in small capacitors of high capacitance byutilizing multiple individual layers of aluminum foil connected to eachpole, the present invention provides a valuable improvement overprevious known capacitors. Use of a conductive polymer, etched aluminumfoil layers, and aluminum oxide on a surface of the aluminum foil layersof at least one pole as a dielectric in some embodiments furtherincreases the capacitance and volumetric efficiency of the presentinvention, making it particularly desirable for bypass applications inhigh power, high speed circuits.

[0030] Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement which is calculated to achieve the same purpose maybe substituted for the specific embodiments shown. This application isintended to cover any adaptations or variations of the invention. It isintended that this invention be limited only by the claims, and the fullscope of equivalents thereof.

1. A capacitor, comprising: a first plurality of layers of aluminum foilconnected to a first electrical terminal of the capacitor; a secondplurality of layers of aluminum foil connected to a second electricalterminal of the capacitor; and a layer of conductive polymer separatingeach layer of aluminum foil, such that each layer of polymer physicallyseparates one of said layers of aluminum foil connected to the firstterminal from one of said layers of aluminum foil connected to thesecond terminal; wherein the first electrical terminal and the secondelectrical terminal are on opposing sides of a capacitor packagecontaining the first and second pluralities of layers of aluminum foil.2. The capacitor of claim 1, wherein the layers of aluminum foil andpolymer are fixed in a flat configuration.
 3. The capacitor of claim 1,wherein the capacitor is bipolar.
 4. The capacitor of claim 1, whereinthe layers of aluminum foil and polymer are fixed in a multiterminalpackage format.
 5. The capacitor of claim 4, wherein the firstelectrical terminal of the capacitor comprises at least two alternatingpins of the multiterminal package, and wherein the second electricalterminal of the capacitor comprises at least two alternating pins of themultiterminal package.
 6. The capacitor of claim 1, wherein the layersof aluminum foil and polymer are fixed in a surface mount capacitorconfiguration.
 7. The capacitor of claim 1, wherein the polymer is aconductive organic polymer.